Angiographic images acquired with X-ray diagnostic apparatuses can facilitate observation of blood vessels. With such angiographic images, medical treatment planning and operations can be conducted based on detailed information on blood circulatory systems in a heart and/or a brain. Such angiographic images are used, for example, in operations such as for removal of emboli in blood vessels, removal of aneurysms, and dissolution of stenosis with indwelled stents. In these operations, the angiographic images are used to confirm the form of blood vessels, focuses, postoperative blood flow, and the like. The operations with use of angiographic images are performed by using a catheter inserted from a blood vessel of a region such as a femoral region and a cervical region. As compared with general surgical operations, the operations using angiographic images have little burden on patients and provide high Quality Of Life (QOL). This makes the angiography an indispensable clinical technique.
A digital subtraction angiography (DSA) is known as a technique for acquiring angiographic images by X-ray diagnostic apparatuses. The DSA is to obtain a difference between a pre-contrasting image (hereinafter referred to as a mask image) and an image after introduction of a contrast medium (hereinafter referred to as a contrast image) so that the contrast medium introduced into blood vessels of a patient is highlighted for clear visualization of the blood vessels.
According to the DSA image (hereinafter referred to as an angiographic image) obtained from the difference between the mask image and the contrast image, not only the form of blood vessels can be acquired, but also various information pieces, such as blood flow velocities and blood flow rates, can be acquired based on transmit time of the contrast medium, and the like. For example, dynamics of the injected contrast medium can be captured by creating a Time Density Curve (TDC) based on signal strength of each pixel of angiographic images. Based on the TDC, various information pieces can be acquired, such as Time to Peak (TP) which represents the time when the concentration of the contrast medium in each pixel becomes a maximum, Arrival Time (AT) which represents the time when the contrast medium starts to dye, and Mean Transit Time (MTT) which represents a mean passing time of the contrast medium. For visually displaying these various information pieces, there is a method called parametric imaging (PI) which images various parameters, such as aforementioned TP, AT, and MTT. The PI provides a technique to generate color maps which express various parameter information in the form of change in color and/or brightness.
However, in DSA imaging, X-rays are emitted like a pulse to enable tens of images to be taken in one second. In the DSA imaging, imaging is performed with a relatively high X-ray intensity for the purpose of reducing noise and providing a high contrast resolution. Furthermore, PI images are acquired by successive observation of the dynamics of the contrast medium in blood vessels. Therefore, it takes longer time to perform the DSA imaging, which increases a radiation dose of the patient. In operations relating to blood vessels and/or a circulatory system, DSA imaging needs to be performed at least twice, once before treatment and once after treatment. This also causes undesirable increase in the radiation dose.
Accordingly, an X-ray diagnostic apparatus with a low X-ray radiation dose is demanded.